Hours after narrowly failing to murder Margaret Thatcher in the Brighton bomb, the IRA calmly announced: “Today we were unlucky, but remember we only have to be lucky once – you will have to be lucky always.”

The blunt language of the IRA’s claim of responsibility seems unimaginable in today’s world of carefully crafted political statements.

But it was a measure of the depth of hatred that fuelled the most toxic of the political struggles Mrs Thatcher engaged in during more than a decade in Downing Street.

While there were other bitter domestic stand-offs, not least the miners’ strike, with the IRA it was deadly and it was personal.

Although the prime target of the bomb that ripped through the Grand Hotel in Brighton during the Conservative Party conference in 1984, survived, five others were killed and more than 30 were injured, many of them maimed for life.

Her reaction was characteristically defiant. Addressing the conference on the same day as the IRA’s warning, she told them: “All attempts to destroy democracy by terrorism will fail.”

And yesterday, almost 30 years on, while many old enemies in Northern Ireland have been reconciled and the IRA relegated to history – officially, at least – the bitterness of that era was still evident.

While other former political opponents lined up to pay tribute to Lady Thatcher, Gerry Adams, the Sinn Fein president, was conspicuous in the vehemence of his comments, accusing the former Prime Minister of inflicting “great hurt to the Irish and British people”.

Even before becoming Prime Minister in 1979, for Margaret Thatcher, the Troubles of Ulster were a personal matter.

Shortly before her election, her close political ally Airey Neave – who as a wartime intelligence officer escaped from the Nazi prison camp at Colditz – was blown up by the INLA in a Palace of Westminster car park.

He had been a prominent supporter of strong security tactics and the experience only served to strengthen her belief that any future settlement would require nothing less than the defeat of the IRA.

In 1981, as republican inmates in the Maze prison outside Belfast staged hunger strikes demanding recognition for their “political” status, the Prime Minister’s response was withering.

“Crime is crime is crime,” she said. “It is not political.”

The 10 prisoners, including Bobby Sands, who went on to starve themselves to death are still regarded in republican circles – and countries such as Cuba – as political martyrs and heroes.

Yet the IRA always held Lady Thatcher responsible for their deaths. It was a theme Gerry Adams returned to yesterday, when he spoke of what he called her “shameful role” in the “epic hunger strikes”.

Then on October 12, 1984 came the Brighton bomb.

The narrowness of the Prime Minister’s escape was made clear when it was later claimed that she had only left the bathroom of the suite seconds before it was blown up.

Others were not so lucky. Among the five killed were Sir Anthony Berry, the Tory MP for Enfield Southgate, and Roberta Wakeham, wife of the then Parliamentary Secretary to the Treasury, John Wakeham.

Lord Tebbit being rescued from the rubble of the Grand Hotel

One of the most enduring images of the atrocity was the television footage of Sir Norman Tebbit, now Lord Tebbit, who was then the trade secretary, being carried on a stretcher from the rubble, barefoot and wearing his pyjamas.

His wife, Margaret, has been confined to a wheelchair ever since.

Lady Thatcher was – characteristically – still at work in her suite on the first floor of the hotel when the bomb exploded at 2.54am.

She had just completed her conference speech for the next day when Robin Butler, her private secretary, came in to hand her a last official paper outlining plans for the Liverpool Garden Festival.

Moments later, as she handed it back complete with her comments, an explosion rang out, followed by a deathly calm and the sound of falling masonry.

Walking across the landing, she called in to the room where a team of secretaries had been finishing typing up the speech to check they had not been harmed.

One of them, who had been using a photocopier at the time, had received an electric shock but was not badly hurt.

Their main concern, Lady Thatcher later recounted, was to reassure her that the speech, which had not yet been fully typed up, was still in one piece.

“It’s all right, we’ve got the speech,” they insisted, handing her a copy for her briefcase.

The bathroom adjoining the Prime Minister’s suite, where she had been moments before, was badly damaged, although in her memoirs she said that, had she been in there at the time, the worst she would have suffered would have been only cuts and bruises.

“Those who had sought to kill me had placed the bomb in the wrong place,” she remarked.

Yet despite her dry response, she made no secret of how close she had come to being killed.

A few days after the attack, she spoke movingly of the experience of going to church for a Sunday service and seeing sunlight streaming through the window on to a floral display.

“This is a day I was not meant to see,” she remarked simply.

But it was be her defiant return to the conference floor the day after the bombing that would be best remembered.

It was not just an attempt to disrupt the party conference, she insisted, but an attempt to subvert a democratically elected government.

“That is the scale of the outrage in which we have all shared,” she said.

“And the fact we are gathered here, now, shocked but composed and determined, is a sign not only that this attack has failed, but that all attempts to destroy democracy by terrorism will fail.”

When she visited the province after that, danger was never far away.

She travelled in convoys of three helicopters – including one “decoy” – that swayed from side to side to avoid surface-to-air missiles smuggled to the IRA from Colonel Gaddafi’s Libya.

After one particularly choppy flight, in which the Prime Minister’s helicopter had skimmed the treetops en route to an engagement in County Fermanagh, her straight-talking press secretary Sir Bernard Ingham, stepped off looked visibly relieved. “That’s the first time I’ve ever flown underground,” he remarked to Deric Henderson, the Press Association’s Ireland editor, who was equally relieved to have landed safely. “Even the cows ducked.”

Lady Thatcher was determined to deny republicans what she called the “oxygen of publicity”, banning the voice of Gerry Adams and others from the airwaves.

An old community centre in Enniskillen lying in ruins the morning after the IRA bombing of 1987

Among the many atrocities of the era was the 1987 Enniskillen bombing when 11 people were murdered by a bomb as they observed Remembrance Sunday – an outrage that left the Prime Minister visibly moved.

The following year, one of the most vicious spirals of violence erupted in the wake of the SAS operation in Gibraltar, in which three IRA terrorists were shot dead as they prepared to set off a car bomb.

It was an unusually public glimpse at the ruthless tactics the security forces were prepared to engage in to stop the IRA during the Thatcher years.

Questions over an RUC “shoot to kill policy” will linger for future historians.

But so too will questions over the extent of a so-called “back channel” of communications with republicans which, in time, opened the way for talks.

And for all her defiance against republican terrorism, Mrs Thatcher’s relationship with the troubled province was far from one-dimensional.

She infuriated the Unionists, who might have been her most natural political ally, only a year after the Brighton bomb by signing the Anglo Irish Agreement, giving the Republic of Ireland a greater say north of the border.

Protestant youths even burnt the Prime Minister's effigy on their July bonfires, accusing her of betrayal.

Yet it was, as the Irish Taoiseach Enda Kenny said yesterday, the moment which laid the foundations for the peace process which would follow.

Lady Thatcher had been, he said, a formidable political leader who had “defined an era in British public life”.

“While her period of office came at a challenging time for British-Irish relations, when the violent conflict in Northern Ireland was at its peak, Mrs Thatcher signed the Anglo-Irish Agreement, which laid the foundation for improved North-South cooperation and ultimately the Good Friday Agreement,” he said.”